February 28: Severe Weather Ahead, Daily Links

WEATHER

Scattered showers and thunderstorms are making their way through the Midstate this morning as even warmer and muggier air makes its way into area. There’s an outside chance that a storm or two could become severe, but in general just expect some briefly heavy rain and some rumbles of thunder.  The HRRR model’s radar simulation has a good handle on the pattern:
hrrr_2017022812_ref_nashville
The storm chances will diminish this afternoon, allowing temperatures to warm up to the upper 60s and low 70s:
tuesday-highs
The more sun you see, the warmer you’ll be!  If my math is right (always questionable) we need to hit 73° today to tie the warmest February on record in Nashville (51.4° in 1882).  We’re also locked into this being the 5th warmest winter (Dec-Jan-Feb) on record…I think the highest we could go is a tie for 4th place.

March is going to roar in like a lion — severe weather is looking increasingly likely Wednesday morning into early afternoon, but that still depends on the specific timing.  The various forecast models are still showing some discrepancies, but the more-accurate models seem to be zeroing in on a mid-morning to early-afternoon window for the greatest threat.  The 3km-NAM model’s radar simulation (don’t worry about the model name, just throwing it in for the weather nerds) shows what I think is a reasonable scenario:
nam3km-refcmp-us_ov-2017022800-loop
That depiction is very similar to the RPM model and the European model in terms of timing, which increases my confidence in its accuracy.  Whenever you see a line of storms like that, it means that damaging winds will be the primary threat, but isolated tornadoes and hail will also be possible, especially once the atmosphere warms up after 9am:
paul-severe-risk-graph
The Storm Prediction Center has outlined an “Enhanced Risk” (level 3 of 5) of severe thunderstorms for roughly the eastern two-thirds of the Midstate, with the remainder of the area in a “Slight Risk” region (level 2 of 5):
paul-severe-risk-region

Okay, there’s some serious nerdiness in this upcoming paragraph — you’ve been warned.  (This is all to give you a better idea of the thought process that goes into producing a complicated severe weather forecast.)  The SPC’s short-range ensemble forecast (SREF) model is a blend of 27 different models — basically, it helps smooth out the differences among the various possibilities.  The SREF is showing a 70+% chance of storms with severe ingredients in the Midstate after 9am tomorrow:
sref_prob_combined_supercell__f033-feb28
Okay, but to what degree will those ingredients favor severe thunderstorms…barely sufficient, over-the-top, or somewhere in between?  That’s measured by a statistic called the “Supercell Composite Parameter” — tomorrow’s storms will be ongoing in an environment where the SCP will be between 6 and 9.  Anything over 6 is bad:
sref_sccp_median_mxmn__f033-feb28
As I said above, damaging straight-line winds (gusts over 60 mph) will be the primary concern tomorrow.  We can get an idea of how widespread the wind threat will be by looking at the “Derecho Composite Parameter” — a derecho is a prolonged damaging wind event that extends over hundreds of miles.  The DCP is forecast to be around 3, which is borderline for that specific phenomenon…but it still indicates a significant straight-line wind threat on a local basis:
sref_derecho_median_mxmn__f030
That said, the “Signifiant Tornado Parameter” (that one should be self-explanatory) will be around 2…which is the threshold at which we start fidgeting a bit:
sref_sigtor_median_mxmn__f030-feb28

All of that might sound scary…but don’t freak out!  As I’m typing this (around 8am), we’re still 24 hours away from all of this ramping up.  There’s plenty of time for things to change — our best hope is that the models are wrong, and that the storms arrive earlier…or that the severe weather ingredients don’t come together just right.  Plan on staying weather-aware throughout the day on Wednesday — you can download our 4WARN mobile app at this link.  Once it’s on your phone/tablet, go to “Settings” under the drop-down menu:
4warn2
Then turn on the Severe Weather Alerts:
4warn1
You can follow us on Twitter as well (Facebook is essentially useless for severe weather information) — links are at the bottom of this post.

After the active weather on Wednesday, we’ll settle into a calmer weather pattern…cooler and drier for Thursday and Friday, then warming back up over the weekend!
wsmv-4-plus-4-am

 

LINKS

 

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Social media links

Twitter: @WSMVweather, @PaulHeggenWSMV, @WSMVLisaSpencer, @WSMVDanThomas, @daphne_deloren, @NWSNashville

Facebook: 4WARN Weather, Paul Heggen WSMV, Lisa Spencer, Dan Thomas WSMV, Daphne DeLoren, NWS Nashville

Instagram: PaulHeggenWSMV

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About paulheggen33

Morning meteorologist for WSMV-TV in Nashville.
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